We are engaged in analysis of the lytic replication of two human herpesviruses: herpes simplex virus (HSV) and Epstein-Barr virus (EBV). We are studying the purified protein products of the viral genes that participate in DNA replication in lytically-infected cells, using both biochemical and molecular genetic approaches to understand the function of these polypeptides in detail. Our recent results regarding HSV proteins can be summarized as follows: 1) UL9, the viral protein that presumably initiates DNA replication, binds to its cognate binding site with a stoiciometry of two polypeptides per binding site; 2) The products of the HSV genes UL5, UL8, and UL52 form a three-polypeptide complex that has both helicase and primase activities. We have shown that UL52 contains the active site for primase catalysis; 3) The HSV DNA polymerase consists of a stable complex of two polypeptides: UL30, the catalytic subunit, and UL42, an accessory subunit that increases the processivity of the enzyme. We have mapped the changes that occur in the interaction between the DNA polymerase and a primer template in the presence of UL42; and 4) We have overexpressed the EBV homologs of the HSV replication proteins and are beginning biochemical analysis of these proteins.